Nitro (—NO2) compounds, particularly nitro aromatic and heterocyclic derivatives, are important industrial chemicals, with an estimated annual production of greater than 108 tons (Kulkarni and Chaudhari 2007). Their applications span a broad range such as food additives, pesticides, herbicides, polymers, explosives, and dyes (Ju and Parales 2010). The nitro group is also an important functional unit in pharmaceuticals such as chloramphenicol, nilutamine, tolcapone, metronidazole, and the recently approved anti-tuberculosis drug delamanid (Martino et al. 2003). Its therapeutic relevance is further illustrated by nitro-containing lead drug candidates such as 9-nitro-noscapine for the treatment of multidrug resistant cancers (Aneja et al. 2006) and 5-nitro-2-furancarboxylamides in treating neglected parasitic protozoa infections (Zhou et al. 2013).
Aromatic nitration is a widely used organic reaction (Yan and Yang 2013). Industrial scale reactions usually include a mixture of nitric acid and sulfuric acid or sometimes nitric acid with other acids. In these reactions, the nitronium ion, NO2+, is believed to be the active species, albeit the potential minor contribution of a radical mechanism (Olah et al. 1978). Currently used methods and materials present several challenges, such as poor selectivity, low yield, generation of multiple isomers and by-products, and low functional group tolerance frequently occur and limit their uses in generating products with specific requirements. In addition, currently used methods are not environmentally sound. Accordingly, there is a need to develop environmentally benign, selective, practical and efficient direct aromatic nitration approaches.